1. Field of the Invention
The present invention relates to a power supply device and a method of controlling the power supply device, and more particularly, to a power supply device having an inrush current protection circuit, a power factor correction (PFC) circuit and an overvoltage protection circuit and a method of controlling the inrush current protection circuit, the PFC circuit and the overvoltage protection circuit.
2. Description of the Related Art
A three-phase motor is a motor having a plurality of windings which are arranged around a rotor and which receive energy from a three phase voltage to rotate the motor. As shown in FIG. 1, a power supply device which obtains a three-phase voltage necessary for driving a motor 200 via input terminals U, V and W of the motor 200, comprises an AC power supply 100 which supplies a commercial AC power, such as for example, (AC 110/220V), a rectifier 300 which rectifies the AC power output from the AC power supply 100, a capacitor CDC which smoothes a voltage rectified by the rectifier 300, an inverter 120 which inverts a DC power output from the capacitor CDC to an AC power having various frequencies and outputs a three-phase voltage. The power supply device may further comprise an inrush current protection circuit 140 which prevents an inrush current into the capacitor CDC during an initial supply of power, a power factor correction (PFC) circuit 150 which maintains an output voltage from the capacitor CDC at a constant value, and an overvoltage protection circuit 130 which protects the capacitor CDC from an overvoltage.
In the inverter 120, a pulse width modulation (PWM) part (not shown) generates a PWM control signal and a plurality of transistors are turned on/off according to a square wave signal of the PWM part. The power supply device comprises a controller (not shown) which controls the output frequency thereof so as to control a rotation speed of the motor 200 and turns on/off an output of the inverter 120 by turning on/off the transistors according to the PWM control signal.
The inrush current protection circuit 140 comprises an inrush current protection resistor Rs provided between the rectifier 300 and the capacitor CDC and connected to the capacitor CDC. A relay part 142 comprises first, second and third contacting points 142a, 142b and 142c. When the relay part 142 connects the first contacting point 142a with the third contacting point 142b, the inrush current protection resistor Rs connects the capacitor CDC with the rectifier 300, which allows power rectified by the rectifier 300 and charged to the capacitor CDC to be limited by the resistor Rs, to prevent the capacitor CDC from being broken down by excessive inrush current in an initial supply of power.
The PFC circuit 150 comprises a PFC switching unit SPFC such as a field effect transistor, a PFC diode DPFC provided with a cathode connected to the capacitor CDC and an anode connected to a node 151 of the PFC switching unit SPFC, and a PFC inductor LPFC provided between the node 151 and the rectifier 300. Herein, the PFC inductor LPFC is disconnected from the rectifier 300 when the relay part 142 connects the first contacting point 142a with the third contacting point 142c, and connected to the rectifier 300 when the relay part 142 connects the second contacting point 142b with the third contacting point 142c. The PFC circuit 150 maintains a voltage applied across the capacitor CDC at a constant value by turning on/off the PFC switching unit SPFC in driving the motor 200, and improves a power factor by making an input current input to the PFC circuit 150 have a same phase as a phase of an input voltage.
The overvoltage protection circuit 130 is connected in parallel with the capacitor CDC, and provided with an overvoltage protection switching unit SOV connected in series with a parallel combination of an overvoltage protection diode DOV and an overvoltage protection resistor ROV. As to the overvoltage protection circuit 130, if the voltage applied across the capacitor CDC is increased and reaches a predetermined overvoltage region due to a voltage regenerated through the inverter 120 from the motor 200 in driving the motor 200, the overvoltage protection switching unit Sov is turned On, to thereby prevent the capacitor CDC from being broken down by an overvoltage.
In the conventional power supply device shown in FIG. 1, the inrush current protection circuit 140 functions until a voltage charged in the capacitor CDC reaches a reference charging voltage after power is initially applied from the AC power supply 100. The inrush current protection circuit 140 becomes unnecessary after a voltage charged in the capacitor CDC reaches the reference charging voltage.
Since the PFC circuit 150 operates after the voltage applied across the capacitor CDC is stabilized (i.e. sufficiently charged), operation of the PFC circuit 150 is not necessary while the inrush current protection circuit 140 operates.
Since the overvoltage protection circuit 130 operates only while the voltage applied across the capacitor CDC is increased by the voltage regenerated from the motor 200, operation of the overvoltage protection circuit 130 is not necessary while the inrush current protection circuit 140 operates (i.e., in an initial charging period), or while the PFC circuit 150 operates after the voltage applied across the capacitor CDC is stabilized.
Since large capacity components are used in the inrush current protection circuit 140, the overvoltage protection circuit 120 and the PFC circuit 150, a size of a product including the conventional power supply device shown in FIG. 1 is increased. Eliminating one or more of the large capacity components would result in a reduction in the product size and a decrease in manufacturing cost.